METHOD AND SYSTEM FOR PRODUCING A THREE-DIMENSIONAL STRUCTURE

Description

[0001] The invention relates to a method for producing a three-dimensional structure from a 3D-printable plastic material using a 3D printing head. The invention also relates to a system for carrying out the method.

[0002] With the help of additive manufacturing processes, components of almost any shape can be manufactured using a suitable material. 3D printing using a 3D printer is a well-known example of additive manufacturing. A 3D printer prints a meltable material, such as a thermoplastic, layer by layer, resulting in a three-dimensional component or structure.

[0003] The stiffness and strength of a component manufactured on this basis depends significantly on the corresponding material properties of the meltable material used. Especially with a view to lightweight construction, it is often desirable for components to be made of fiber-reinforced composites in order to achieve high, region-specific strength and stiffness. Fiber-reinforced composites exhibit anisotropic material properties, meaning that strength and stiffness are direction-dependent and thus dependent on the fiber orientation.

[0004] The integration of fiber material into 3D printing on demand would have the decisive advantage of enabling components and structures to be produced whose load paths are precisely adapted to the conditions without requiring unnecessary material.

[0005] From the subsequently published DE 10 2017 124 3526, a 3D printing head (including corresponding system and method) is known, to which a virtually endless fiber material is fed. Furthermore, plastic material is fed to the 3D printing head with the aid of three or more feed channels, with the fiber material and plastic material opening into a common mixing chamber, whereby the passing fiber material is wetted by the plastic material and dispensed in this form. This allows the development of almost any structure with integrated load paths. From the subsequently published DE 10 2017 124 353, a system with a 3D printing head is also known, wherein the inlet of the material feed to the 3D printing head is hermetically sealed with a pressure source in order to prevent the thermal matrix material from escaping at the inlet of the material feed.This prevents rising plastic material from escaping above the 3D printing head.

[0006] However, when creating complex structures and components, it has proven disadvantageous that the molten plastic extruded from the 3D printing head cools and hardens only slowly, which makes it difficult to create cantilevered structures in space. For example, with the 3D printing heads described above, depending on the plastic material, it is rarely possible to print freely upwards in space, as the extruded plastic material does not cool and harden quickly enough to adequately support the upwardly printed structure, unless the speed of the 3D printing head is adjusted accordingly, which would result in an extremely slow printing process. However, if the plastic material is not cooled and solidified in time, the cantilevered structure would not be load-bearing.

[0007] In practice, it is therefore known that the components or the structure to be manufactured are actively cooled using external cooling systems, such as a fan, in order to reduce the cooling time and achieve a faster overall printing phase. However, it has been shown that such external active cooling of the component or the structure to be manufactured is not sufficient to reliably and efficiently print a self-supporting structure vertically.

[0008] DE 10 2014 006 706 A1 discloses a method and system for producing a two-dimensional or three-dimensional framework with rods made of a composite material with fibers and a matrix. The fiber material and the matrix material are mixed and extruded using an extruder unit. A cooling tube is provided at the outlet opening, and a fan directs the ambient air through the cooling tube and directly to the plastic material exiting the extruder unit's outlet opening.

[0009] EP 3 106 290 A1 relates to a 3D printing method and a 3D printing device for applying a material, in particular a metallic material, to a surface. An area in front of the print head is locally heated with a heating element. The applied material and optionally the surface are cooled again with a cooling element. The heating element and / or the cooling element can be arranged and aligned in the direction of movement of the print head. The gas quantity and temperature of the heating and cooling elements can be regulated by a control device.

[0010] US 2016 / 0207263 A1 discloses a device for layer-by-layer 3D printing with a print head and a heating and cooling device. To improve the cohesion between two model layers, a hot air stream is directed onto the print area of the print head, which heats the model layer just created. Support layers made of a support material are inserted between the model layers to accommodate overhangs. To facilitate later removal of such support layers from the finished component, a cooling air stream is directed onto the print area of the print head during a transition from a support layer to a model layer in order to reduce the cohesion between the model layer and the support layer. The activation of cooling elements of the cooling device can be controlled by a controller, for example, depending on the current or planned direction of movement of the print head.

[0011] WO 2016 / 088048 A1 describes a cooling device for a nozzle of a 3D printing head. Nozzle cooling is intended to stop the flow of liquid printing material from the nozzle by solidifying it more quickly and precisely, thus enabling faster switching between different printing materials.

[0012] However, it has been shown that, especially in the production of continuous fiber-reinforced 3D-printed structures, in which the 3D-printable plastic material is mixed together from a virtually continuous fiber material and a matrix, cooling in the component edge areas is an important factor to ensure that the fiber can be deposited at high speed, especially at acute angles. Otherwise, after deposition of radii, the component corners may become worn, i.e., the fiber is pulled out of the corner, specifically in places where the plastic has not yet solidified.

[0013] It is therefore an object of the present invention to provide an improved method and an improved system in which, in particular, quasi-continuous fiber-reinforced 3D-printed structures can be produced more quickly and efficiently without damage to the structure to be produced due to the printing speed.

[0014] The object is achieved according to the invention with the method according to claim 1 and the system according to claim 10.

[0015] According to claim 1, a method for producing a three-dimensional structure from a 3D-printable plastic material using a 3D printing head is proposed. A 3D-printable plastic material is first fed to the 3D printing head and then extruded from an outlet opening of the 3D printing head by means of the 3D printing head. The extruded plastic material is cooled by means of a cooling device by directing at least one fluid stream onto the extruded plastic material.

[0016] The 3D print head can be configured such that a 3D-printable plastic material with and without reinforcing fibers can be fed into it. The 3D print head can also be configured to receive a fiber material and a matrix material separately as 3D-printable plastic material, wherein the fiber material is then mixed with the matrix material to form a fiber-reinforced plastic material within the 3D print head. Furthermore, the 3D print head and the method can be configured to melt the plastic material with the aid of a heating device so that it can be extruded in a viscous or thick form with the aid of the extruder. It is advantageous if, in particular, a solid material is fed to the 3D print head, which is then melted with the aid of the 3D print head and a corresponding heating device.

[0017] The 3D-printable plastic material can, in particular, be a thermoplastic plastic with or without fiber reinforcement. The 3D-printable plastic material can therefore also be a quasi-continuous fiber-reinforced composite material in which a matrix material, for example a thermoplastic matrix material or a thermosetting matrix material, is combined with a quasi-continuous fiber material and thus dispensed. However, it is also conceivable that the 3D-printable plastic material is a plastic material without fiber reinforcement and thus does not contain a quasi-continuous fiber material. In any case, the 3D-printable plastic material can also be a thermoplastic or thermosetting plastic material without fiber reinforcement. Ultimately, the 3D-printable plastic material includes all plastic materials that can be extruded using a 3D printer and a 3D printing head.

[0018] Furthermore, it is provided that the cooling of the extruded plastic material is varied with the aid of the cooling device with regard to the cooling power and / or the cooling direction, namely during the printing process.

[0019] Unlike DE 10 2014 006 706 A1, the cooling varies with regard to the cooling power and / or cooling direction so that the extruded plastic material can be cooled specifically at the appropriate points, resulting in higher printing speeds and better component quality when printing the three-dimensional structure. The variation in cooling, i.e. the variation in cooling power and / or cooling direction, can be program-controlled using the printing program so that the cooling power and / or cooling direction is varied and changed accordingly when printing the three-dimensional structure in order to cool the just extruded plastic material more and better at precisely those points and to cool it less or not at all in other points that are responsible for fast printing and high component quality.This allows for targeted cooling of those areas of the extruded plastic material where rapid and premature solidification of the plastic material is necessary for process-reliable printing (increasing the cooling capacity in a specific cooling direction). In contrast, those areas of the extruded plastic material that do not require premature solidification, or where premature solidification would be counterproductive, can have their cooling capacity in this cooling direction throttled so that very little or no cooling occurs, thus preventing premature solidification of the plastic material.

[0020] The inventors have recognized that by varying the cooling power and / or cooling direction of extruded plastic materials, particularly in combination with fiber-reinforced 3D-printable plastic materials, the component quality of the three-dimensional structure to be produced can be significantly improved. Furthermore, it is also possible to print in a self-supporting manner in space, since by varying the cooling power and / or cooling direction, the extruded plastic material can be specifically cooled at those points that are essential for the self-supporting structure with regard to rapid solidification. Especially in combination with fiber-reinforced plastic materials, by varying the cooling power and / or cooling direction during printing of the plastic material, damage to the printed structure caused by uncured plastic can be prevented.

[0021] In one embodiment, the cooling is varied depending on a printing position of the 3D print head, a movement direction of the 3D print head, a movement speed of the 3D print head, a movement trajectory (path) of the 3D print head, and / or a structural shape or component shape of the three-dimensional structure to be produced. For example, it is conceivable that increasing the movement speed of the 3D print head increases the cooling performance, preferably significantly, in order to quickly cool the extruded plastic material, particularly shortly after exiting the outlet opening of the 3D print head, and thus significantly accelerate the solidification process of the plastic.However, it is also conceivable that the cooling direction is changed depending on the direction of movement, so that in a first direction of movement, the extruded plastic material is cooled from a first cooling direction, while in a second direction of movement, the extruded plastic material is cooled from a second cooling direction that differs from the first cooling direction. It is also conceivable that the cooling performance in the first cooling direction differs from the cooling performance in the second cooling direction.

[0022] It is also conceivable that the cooling power and / or cooling direction are varied depending on the position of the 3D print head, particularly with regard to the position of the component or structure to be manufactured, so that the desired cooling power and / or cooling direction is specifically set at the correspondingly specified positions of the component structure. This can, for example, be included in the program data for controlling the 3D print head, so that the cooling power and / or cooling direction specified at this point is set by the 3D print head through feedback of the position of the 3D print head with regard to the structure to be printed. In this case, the position of the 3D print head serves as feedback for the current printing position within the component and the desired cooling.

[0023] Depending on the structural shape of the three-dimensional structure to be produced, the cooling can be varied in terms of cooling power and / or cooling direction, allowing the cooling power and / or cooling direction to be adjusted specifically at those points that are critical for the printing process. When the 3D print head moves to the appropriate position within the three-dimensional structure to be printed, the cooling power and / or cooling direction are then adjusted according to the cooling specifications.

[0024] In a further embodiment, the cooling performance of the cooling system is varied by controlling the temperature of the fluid flow, by changing the volume flow of the fluid flow, and / or by changing the shape of the fluid flow of the cooling fluid. For example, it is conceivable that a gaseous fluid is used as the cooling fluid, which is directed at a fluid flow velocity onto the extruded plastic material to be cooled, wherein the cooling fluid is first cooled below the ambient temperature. The cooling fluid thus has a lower temperature than the ambient temperature, which can increase heat dissipation and cooling performance. It is conceivable that the temperature of the cooling fluid is varied accordingly during the printing process in order to vary the cooling performance.

[0025] It is also conceivable, however, that the volume flow is varied to vary the cooling performance, where the volume flow here means the volume of fluid per unit of time. By increasing the volume flow, i.e. the amount of fluid per unit of time, the cooling performance can also be increased, since more heat can generally be removed from the extruded plastic material per period of time. Varying the volume flow represents one of the simplest ways of varying the cooling performance. It is of course also conceivable that the cooling performance can be varied by changing the shape of the volume flow, for example by adjusting a nozzle to fan out the fluid flow or to concentrate it on the extruded plastic material.

[0026] In a further advantageous embodiment, the cooling direction is varied by changing the angle of the fluid flow relative to the extruded plastic material, so that the extruded plastic material is exposed to the fluid flow from different directions. The cooling of the 3D printing head can be configured such that the extruded plastic material is exposed to a first cooling direction at a first time and to a second cooling direction, which differs from the first cooling direction, at a second time following the first time, thereby changing the angle of flow.The object of the invention is further achieved in that the 3D printing head is designed such that the nozzle arranged on the 3D printing head for dispensing the fluid flow is arranged to be movable around the extruded plastic material, so that the cooling direction can be changed from the first cooling direction to the second cooling direction by moving the nozzle.

[0027] The cooling capacity can also be adjusted accordingly, so that a first cooling capacity is provided in the first cooling direction, while a second cooling capacity is provided in the second cooling direction. Consequently, the cooling capacity and the cooling direction can also be varied simultaneously.

[0028] In a further embodiment, if more than one fluid stream can be directed onto the extruded plastic material, the cooling direction can be varied by switching one or more of the fluid streams on or off in order to thus vary the cooling direction. This is advantageous, for example, if the 3D printer has two or more fluid nozzles that are rigidly arranged, for example, on the 3D print head and direct their respective fluid streams onto the extruded plastic material from a predetermined cooling direction. At a first point in time, all fluid streams from all nozzles can be directed onto the extruded plastic material, while at a second point in time, one or more of the fluid streams can be switched off, so that the extruded plastic material is then only supplied with fluid from those cooling directions whose fluid streams are not switched off.

[0029] In a further embodiment, with an arcuate movement trajectory of the 3D printing head, the extruded plastic material is cooled such that at least one fluid stream is directed towards an inner side of the arcuate movement trajectory onto the extruded plastic material. It is particularly advantageous if the at least one fluid stream directed towards the inner side of the arcuate movement trajectory onto the extruded plastic material has a higher cooling capacity than a fluid stream directed towards an outer side of the arcuate movement trajectory opposite the inner side onto the extruded plastic material. The inner side of an arcuate movement trajectory is the side facing the center of a radius of the arcuate movement trajectory. The outer side is therefore the side facing away from the center.By appropriately cooling the inside of the arc-shaped movement trajectory on the extruded plastic material, the solidification process can be significantly accelerated, preventing the reinforcement fibers contained in the 3D printable plastic material from tearing out during further printing. Further printing creates a tensile force on the virtually endless fiber material within the extruded plastic material, which can lead to so-called "stripping" especially on the inside of the arc. By specifically cooling this inside of the arc-shaped movement trajectory, the rapid solidification of the plastic material can prevent the reinforcement fibers from tearing out.

[0030] In a further advantageous embodiment, the extruded plastic material is cooled by the cooling device from a first cooling device with a first fluid flow and from a second cooling direction opposite the first cooling direction with a second fluid flow, so that the extruded plastic material is cooled from at least two sides. This allows for very high heat dissipation, which is particularly necessary for structural stability in freestanding printing, especially vertically.

[0031] In a further embodiment, the extruded plastic material is further cooled from a third cooling direction with a third fluid flow and then from a third, opposite, fourth cooling direction in the fourth fluid flow, wherein the third cooling direction runs at an angle, preferably 90°, to the first cooling direction. Thus, the extruded plastic material is cooled from four sides with a fluid flow, allowing even free-floating structures to be printed quickly and efficiently.

[0032] In an advantageous embodiment, the fluid flows of adjacent cooling directions can be adjusted by the cooling device in such a way that, due to the fluid flows, a force with a force vector acts on the extruded plastic material, the origin of which lies between the two cooling directions of the fluid flows. Depending on the control system, this can achieve an inflow that acts as if a cooling nozzle were present between the actually present cooling nozzles.

[0033] The object is further achieved with the system according to claim 10 for producing a three-dimensional structure from a 3D-printable plastic material, wherein the system has a 3D printing head to which a 3D-printable plastic material can be fed via a feed device. The 3D printing head further comprises an extruded unit which is designed with an outlet opening for extruding the plastic material fed to the 3D printing head. In addition, the 3D printing head has a cooling device which is designed to cool the extruded plastic material by means of at least one fluid stream directed onto the extruded plastic material. According to the invention, it is provided that the cooling of the extruded plastic material by means of the fluid stream is varied with regard to the cooling power and / or the cooling capacity with the aid of a control device.The control device is designed such that it sets a first cooling power and / or cooling direction at a first point in time, while it sets a second cooling power and / or second cooling direction that is different from the first cooling power and / or first cooling direction at a second point in time following the first.

[0034] Advantageously, the 3D printing head has one or more cooling nozzles designed to discharge the respective fluid stream onto the extruded plastic material in the immediate vicinity of the outlet opening of the extruder.

[0035] According to the invention, it is further provided that the cooling nozzles are movably arranged on the 3D printing head, so that the respective cooling direction can be varied. It is conceivable that the nozzle is arranged so that it can move along a circular path around the extruded plastic material, so that the cooling direction can be changed and varied during the extrusion of the plastic material.

[0036] It is further advantageous if all nozzles of the cooling device with which the respective fluid flow and the extruded plastic material are diverted are arranged on the 3D printing head, so that with any movement of the 3D printing head to position the extruded plastic material, it is ensured that the extruded plastic material is cooled accordingly.

[0037] The invention is explained by way of example with reference to the attached figures.

[0038] They show there: Figure 1- schematic representation of a 3D printing head with fixed cooling nozzles; Figure 2 - schematic representation of a 3D printing head with movable cooling nozzles; Figure 3 Representation of a cooling performance variance.

[0039] Figure 1 schematically shows a part of a 3D printing head 1, which is referred to below as a 3D printing head. The 3D printing head has an extruder unit 2, which is configured to extrude a 3D-printable plastic material fed to the 3D printing head 1 at an outlet opening 3. In Figure 1 It is schematically shown that a 3D-printable plastic material 4 can be fed to the 3D printing head 1 and the extruder unit 2.

[0040] The plastic material 4 can, for example, contain a fiber reinforcement in the form of a quasi-endless fiber material that is provided inside the plastic material 4. This can be achieved by supplying such a material to the 3D printing head 1. However, it is also conceivable that in a Figure 1 In a part not shown, both the plastic material and the fiber material are fed separately to the 3D printing head 1 and then mixed accordingly in a mixing chamber, as is known, for example, from the subsequently published DE 102017 124 352.6.

[0041] A cooling device 5 is provided radially encircling the outlet opening 3 of the extruder unit 2, comprising a total of four cooling nozzles 6. These cooling nozzles are arranged centrally around the outlet opening 3 and, in particular, such that two cooling nozzles 6 are always arranged opposite one another, and an angle of 90° is formed between two adjacent cooling nozzles. The cooling nozzles 6 point from the outside inward toward the outlet opening 3, so that the plastic material extruded from the outlet opening 3 is directly exposed to a fluid flow and thus actively cooled.

[0042] Connections 7 can be provided so that a cooling fluid can be supplied to the cooling device 5, which is then discharged via the cooling nozzles 6.

[0043] The cooling nozzles 6 can be designed such that they can vary the cooling performance and / or the cooling direction in order to adapt the cooling to the specified boundary conditions of the manufacturing process. For example, it is conceivable that some cooling nozzles 6 are switched off, meaning that the fluid flow is directed onto the extruded plastic material only from the cooling nozzles that are still switched on. However, it is also conceivable that the cooling performance is adjusted accordingly by increasing or decreasing the volume flow.

[0044] Figure 2 shows, by way of example, a schematic representation of a 3D printing head 1 in which the nozzle 6 of the cooling device 5 is rotatably arranged on the printing head 1. For this purpose, the printing head has a circular frame 8 on which the cooling device 5 is movably arranged. Figure 2The cooling nozzle 6 can be moved centrally around the outlet opening 3 of the print head 1 by means of the frictional connection 9 shown between the motor 10 and the circular frame 8.

[0045] This makes it possible to control the cooling direction from which the fluid flow hits the extruded plastic material for cooling.

[0046] In this case, it can advantageously be provided that the cooling nozzle 6 is pivotably mounted via a joint 11 in order to cool the extruded plastic material over a larger area or to vary the cooling position. It can also be provided that the position of the nozzle is translationally displaced relative to the outlet opening of the 3D printing head or is designed to be translationally displaceable.

[0047] Figure 3Finally, FIG. 1 schematically shows a section of an extruded plastic material 20 that was deposited by the print head. The extruded plastic material 20 has a fiber reinforcement 21 in the form of a virtually endless fiber material inside, which is intended to reinforce the structure accordingly.

[0048] The extruded plastic material 20 has a first section 22, which lies on an inner side of the arc-shaped deposited extruded plastic material 20 and thus also on an inner side of an arc-shaped movement trajectory of the 3D head. A second section 23 and a third section 24 are located in front of the first section 22, and this third section 24 adjoins the first section 22. Starting from the second section 23, via the first section 22 to the third section 24, the extruded plastic material 20 is printed, with the cooling performance in the first section 22 from the inner side (indicated by the arrow) being higher than in the two remaining sections 23 and 24.The aim of this is to ensure that the plastic material in the first section 22 hardens more quickly on the inside of the arched structure, thereby preventing the quasi-endless fiber material 21 of the extruded plastic material 20 from being pulled out towards the inside during further pressure. List of reference symbols

[0049] 1) 3D printing head 2) Extruder unit 3) Extrusion port 4) Plastic material 5) Cooling device 6) Cooling nozzles 7) Cooling device connections 8) Circular frame 9) Friction connection 10) Motor 11) Joint 20) Extruded plastic material 21) Fiber reinforcement 22) First section 23) Second section 24) Third section

Claims

1. A method of manufacturing a three-dimensional structure from a 3D printable plastic material (4) by means of a 3D print head (1), the method comprising the following steps: - Feeding the 3D printable plastic material (4) to the 3D print head (1) and - Extruding the plastic material (4) fed to the 3D print head (1) from an outlet opening (3) of the 3D print head (1), - wherein the extruded plastic material (4) is cooled by means of a cooling device (5) by directing at least one fluid flow onto the extruded plastic material (4), and - wherein the cooling of the extruded plastic material (4) is varied with respect to the cooling performance and / or the cooling direction by means of the cooling device (5), characterized in that a nozzle (6) arranged movably on the 3D print head (1) for outputting the fluid flow is arranged movably around the extruded plastic material (4), so that the cooling direction can be changed from a first cooling direction to a second cooling direction by moving the nozzle (6).

2. Method according to claim 1, characterized in that the cooling is varied based on a print head position of the 3D print head (1), a direction of movement of the 3D print head (1), a speed of movement of the 3D print head (1), a movement trajectory of the 3D print head (1) and / or a structural shape of the three-dimensional structure to be produced.

3. Method according to claim 1 or 2, characterized in that the cooling performance of the cooling is varied by tempering the fluid flow, by changing the volume flow of the fluid flow and / or by changing the shape of the fluid flow of the cooling fluid.

4. Method according to one of the preceding claims, characterized in that the cooling direction is varied by changing the angle of the fluid flow relative to the extruded plastic material (4).

5. Method according to one of the preceding claims, characterized in that the cooling direction is varied for more than one fluid flow by switching the fluid flows on or off.

6. Method according to one of the preceding claims, characterized in that, during an arcuate movement trajectory of the 3D print head (1), the extruded plastic material (4) is cooled in such a way that at least one fluid flow is directed onto the extruded plastic material (4) in the direction of an inner side of the arcuate movement trajectory.

7. Method according to claim 1 of the preceding claims, characterized in that the extruded plastic material (4) is further cooled by means of the cooling device (5) from a third cooling direction with a third fluid flow and from a fourth cooling direction opposite the third cooling direction with a fourth fluid flow, the third cooling direction running at an angle to the first cooling direction.

8. Method according to claim one of the preceding claims, characterized in that the fluid flows of adjacent cooling directions are adjusted by means of the cooling device in such a way that, due to the fluid flows, a force with a force vector whose origin lies between the two cooling directions of the fluid flows acts on the extruded plastic material.

9. Method according to one of the preceding claims, characterized in that the 3D-printable plastic material (4) is a composite material formed from a quasi-endless fiber material and a matrix material.

10. Installation for producing a three-dimensional structure from a 3D-printable plastic material (4), having a 3D print head (1) to which a 3D-printable plastic material (4) can be fed via a feed device, having an extruder unit (2) which is designed to extrude the plastic material (4) fed to the 3D print head (1) from an outlet opening (3), and having a cooling device (5), which is designed to cool the extruded plastic material (4) by means of at least one fluid flow directed onto the extruded plastic material (4), characterized in that the system is designed to carry out the method according to one of the preceding claims and, for this purpose, one or more of the cooling nozzles (6) are arranged movably on the 3D print head (1), so that the respective cooling direction can be varied.